Set out 4 to 6 small clean glass mason jars or ramekins on a stable surface.

In a heavy-bottomed saucepan, whisk together the sugar, cocoa powder, cornstarch, and sea salt to remove any lumps.

In a separate bowl, whisk together the whole milk, heavy cream, and egg yolks until well combined.

Gradually whisk the milk mixture into the dry ingredients in the saucepan until completely smooth.

Place the pan over medium heat and whisk constantly, scraping the bottom and sides to prevent burning.

Once the mixture thickens and reaches a gentle bubbling boil, continue to whisk vigorously for exactly 1 minute, then remove from heat.

Immediately stir in half of the chopped chocolate (3 oz), the butter, and the vanilla extract. Let sit 30 seconds, then whisk until completely melted and glossy.

Divide the hot pudding evenly among the prepared jars. Cover the surface with plastic wrap to prevent a skin from forming, and chill in the refrigerator for at least 4 hours.

Before serving, roughly chop the extra block of dark chocolate into irregular shards and pile generously on top of each chilled jar.